1. Field of the Invention
The present invention relates to a liquid crystal display device having a crosstalk preventing structure.
2. Description of the Related Art
Such a conventional active matrix liquid crystal display device is known, which has a structure in which pixel electrodes are formed on an overcoat film that covers thin film transistors. In this structure, the data lines and scanning lines which are connected to the thin film transistors are formed under the overcoat film. Therefore, the pixel electrodes formed on the overcoat film are positioned above the data lines and scanning lines and will not short-circuit to these lines. Thus, the edges of each pixel electrode can be positioned to be overlaid above the data lines and scanning lines, making it possible to increase the aperture ratio.
However, in the above-described case, since the structure is such that the data lines and the pixel electrodes are insulated by a single-layer insulating film, a parasitic capacitance is produced therebetween, leading to the occurrence of a so-called vertical crosstalk phenomenon, which leaves lines dragging in the background of a black display.
As a measure for this, a liquid crystal display device described in Unexamined Japanese Patent Application KOKAI Publication No. 2004-341185 has an auxiliary capacitor line between a data line and a pixel electrode. Since a common potential is supplied to the auxiliary capacitor lines, no parasitic capacitance is produced between the data lines and the pixel electrodes, and the vertical crosstalk is thus prevented.
The above-indicated prior document also describes a semi-transmissive reflective liquid crystal display device. In order to have a large ratio of aperture over the total of transmissive and reflective regions, this liquid crystal display device has its auxiliary capacitor electrodes made of high reflectivity metal such as aluminum-based metal, silver-based metal, etc., and has its thin film transistors and their surroundings covered with the auxiliary capacitor electrodes and pixel electrodes. Thereby, the auxiliary capacitor electrodes positioned in the regions corresponding to the thin film transistors and their surroundings function as reflective plates for reflecting external light.
However, the above-indicated prior document does not describe a structure in which auxiliary capacitor electrodes are connected to the outside. Just for an assumption, in a case where auxiliary capacitor electrode connection pads made of the same material (a transparent conductive material such as ITO (Indium Tin Oxide), etc.) as the pixel electrodes are formed on the same layer as the pixel electrodes, the auxiliary capacitor electrode connection pads are to be connected to connection pad portions constituted by a part of the auxiliary capacitor electrodes, through contact holes formed in an insulating film under the auxiliary capacitor electrode connection pads. However, the auxiliary capacitor electrode connection pads made of a transparent conductive material such as ITO, etc. and the connection pad portions of the auxiliary capacitor electrodes made of high reflectivity metal such as aluminum-based metal, silver-based metal, etc. have a large contact resistance with respect to each other, raising a problem that a fine ohmic contact cannot be formed.